1. Field of the Invention
The present invention relates to a conveying apparatus using a conveying belt and a recording apparatus for recording an image on a conveyed object conveyed by the conveying apparatus, which can be preferably utilized in particular for a conveying apparatus for applying a voltage to electrodes provided on the conveying belt to convey the conveyed object while electrostatically adsorbed or attracted to the conveying belt and a recording apparatus provided with the conveying apparatus.
2. Related Background Art
Conventionally, as a recording apparatus of this type, there is known, for example, a recording apparatus such as a printer by an ink-jet method.
In general, an ink-jet recording apparatus is an apparatus for discharging ink from a recording head to record an image on a recording medium. The ink-jet recording apparatus has such advantages that a recording head can be made compact easily, an image of high definition can be recorded fast, running costs are low, noise is less due to a non-impact method and it is easy to record a color image using inks of many colors.
Among all recording apparatuses of this type, an apparatus of a full-line type can realize further high-speed recording, which uses a recording head of a line-type in which a multiplicity of nozzles are arranged in a paper width direction.
However, in the apparatus of a full-line type, a distance from a recording head in a position on the most upstream side to a recording head in a position on the most downstream side becomes rather long. Thus, rising of a recording sheet occurs in a recording area and a jam or a disturbance of a recording image is caused.
Therefore, there is generally known a method of generating an electric force by applying a voltage to electrodes provided on a conveying belt to adsorb or attract the recording sheet so as to urge the recording sheet downward to prevent it from rising.
In such an ink-jet recording apparatus, a recording sheet supplied by a sheet supplying device is conveyed while being adsorbed to an upper surface of a conveying belt and held there by adsorption force generating means provided on the conveying belt, and an image is recorded on a recording area by a recording head.
FIG. 9 is a schematic view showing the configuration of an entire recording apparatus in accordance with a conventional art. The recording apparatus having an automatic sheet supplying device is composed of (I) a sheet supplying unit, (II) a conveying belt unit, (III) a recording head unit and (IV) a sheet discharging unit. Each of these units will be hereinafter described with reference to FIG. 9. (I) Sheet supplying unit
In the figure, a sheet supplying unit 102 has a configuration in which a pressure plate 121 loading a recording sheet P and a supplying rotator 122 supplying the recording sheet P are attached to a base 120. The pressure plate 121 is rotatable around a rotation shaft a combined to the base 120 and is biased to the supplying rotator 122 by a pressure plate spring 124.
In a part of the pressure plate 121 opposing the supplying rotator 122, a separation pad 125 is provided which is made of a material with a large friction coefficient such as artificial leather for preventing double supplying of the recording sheet P.
Moreover, in the base 120, a separation pawl 126 for covering a corner part of loaded recording sheet P in one direction to separate one recording sheet P from another and a not-shown release cam for releasing abutment of the pressure plate 121 and the supplying rotator 122 are provided.
In the above-mentioned configuration, in a waiting state, the release cam presses down the pressure plate 121 to a predetermined position, and then the abutment of the pressure plate 121 and the supplying rotator 122 is released.
In this state, when a driving force of a conveying roller 132 is transmitted to the supplying rotator 122 and the release cam by a gear or the like, the release cam separates from the pressure plate 121 to lift the pressure plate 121, and the supplying rotator 122 and the recording sheet P abut each other.
Then, as the supplying rotator 122 rotates, the recording sheet P is picked up and starts to be supplied, and one sheet is separated from another by the separation pawl 126 to be sent to a conveying belt unit 103.
The supplying rotator 122 continues to rotate until it supplies the recording sheet P into the conveying belt unit 103. Then, the sheet supplying unit turns into a waiting state again in which the abutment of the recording sheet P and the supplying rotator 122 is released, and the driving force from the conveying roller 132 is cut off.
Reference numeral 190 denotes a supplying rotator for hand supplying. The supplying rotator 190 supplies the recording sheet P placed on a hand supply tray 191 in accordance with a record instruction signal of a computer and conveys it to the conveying belt unit 103.
(II) Conveying Belt Unit
The conveying belt unit 103 has a conveying belt 131 for adsorbing and conveying the recording sheet P and a not-shown PE sensor. The conveying belt 131 is driven by a driving roller 134 and is wound and suspended by a conveying roller 132 and a pressure roller 135 that are driven rollers.
Further, the conveying roller 132 and the driving roller 134 are rotatably attached to a platen 130, the pressure roller 135 is rotatably attached to the other end of an arm 150 that is swingably attached to the platen 130 at one end, and applies a tension to the conveying belt 131 by the arm 150 being pressed by a spring 151.
In addition, the platen 130 is positioned below the conveying belt 131 and plays a role of regulating downward displacement of the conveying belt 131.
In a position opposing the conveying roller 132, a pinch roller 133 following the conveying belt 131 is provided abutting the conveying belt 131. The pinch roller 133 becomes in contact with the conveying belt 131 under pressure by a not-shown spring, thereby guiding the recording sheet P to a recording head unit 107.
At an entrance of the conveying belt unit 103 to which the recording sheet P is conveyed, an upper guide 127 and a lower guide 128 for guiding the recording sheet P are arranged. In addition, a PE sensor lever 123 for transmitting detection of a front end and a rear end of the recording sheet P to a PE sensor (not shown) is provided in the upper guide 127.
Moreover, the recording head unit 107 for forming an image based on image information is provided on the downstream side in the conveying direction of a recording sheet of the conveying roller 132.
In the above-mentioned configuration, the recording sheet P conveyed to the conveying belt unit 103 is guided by the upper guide 127 and the lower guide 128 and then conveyed to a roller pair of the conveying roller 132 and the pinch roller 133. At this point, a recording position on the recording sheet P is found by sensing the front end of the conveyed recording sheet P by the PE sensor lever 123.
In addition, the recording sheet P is conveyed by the conveying belt 131 rotating via the conveying roller 132 by a sheet feeding motor to be described later.
(III) Recording Head Unit
The recording head unit 107 is provided with four ink-jet recording heads of line type in which a plurality of nozzles are arranged in a direction perpendicular to the conveying direction of the recording sheet P. These ink-jet recording heads are arranged on a head holder 170 with a predetermined interval in the order of 107K (black), 107C (cyan), 107M (magenta) and 107Y (yellow) from the upstream in the conveying direction of the recording sheet P.
The recording heads 107K, 107C, 107M and 107Y can give heat to ink by a heater or the like. Then, the ink is film-boiled by this heat, and the ink is discharged from the nozzles of the recording heads 107K, 107C, 107M and 107Y by pressure change caused by growth or contraction of bubbles due to this film boiling to form an image on the recording sheet P.
Further, the head holder 170 is rotatably fixed by a shaft 172 at one end, and a protruded portion 171 provided on the other end and a rail 173 engage with each other, whereby a distance (sheet distance) between nozzle surfaces and the recording sheet P is defined.
(IV) Sheet Discharging Unit
A sheet discharging unit 104 is composed of a sheet discharging roller 141 and a spur 142. The recording sheet P on which an image is formed by the recording head unit 107 is nipped and conveyed by the sheet discharging roller 141 and the spur 142 to be discharged to a sheet discharge tray 143.
The rotation force of the driving roller is transmitted by a transmitting-means (not shown) to the discharging roller 141 to be driven.
Further, the external circumference of the spur 142 is formed as a sharpened uneven surface and prevents ink of a recorded image from being transferred by the spur 142 when the spur 142 rolls on a recording surface after an image is recorded.
The mechanism and operations of adsorbing conveyance of a conveying apparatus in accordance with the conventional art will now be described with reference to FIGS. 10 to 13.
FIG. 10 is a schematic view showing a configuration of a conveying apparatus in accordance with the conventional art.
In the figure, reference numeral 131 denotes a conveying belt that moves while adsorbing and holding the recording sheet P. The conveying belt 131 is made of a synthetic resin such as polyethylene and polycarbonate with a thickness of approximately 0.1 mm to 0.2 mm and is formed as an endless belt.
Reference numeral 152 denotes a power feeding brush connected to a high voltage power source (not shown) that generates a predetermined high voltage. The power feeding brush 152 is provided joining the conveying belt 131.
Adsorption force generating means 136 to be described later are provided in the conveying belt 131. When the power feeding brush 152 applies a voltage of approximately 0.5 KV to 10 KV to the adsorption force generating means 136, an adsorption force is generated in the conveying belt 131.
The conveying roller 132, the driving roller 134 and the pressure roller 135 are rollers that support the conveying belt 131 and impart an appropriate tension to the conveying belt 131. The driving roller 134 is combined with a sheet feeding motor 160.
In addition, a sheet pressing roller 140 as pressing means for pressing the recording sheet P on a conveying belt side is rotatably attached to a sheet pressing roller supporting member 139. The sheet pressing roller supporting member 139 is mounted so as to rotate around the rotation shaft of the pinch roller 133. The sheet pressing roller 140 is biased to the conveying belt 131 side by not-shown biasing means.
Reference numeral 138 indicates a cleaning roller pair, which is provided to nip the conveying belt 131 under pressure. The cleaning roller pair is capable of absorbing ink in order to remove stain such as ink stuck to the conveying belt 131 and is formed of a sponge of continuous vesicles with a small diameter (preferably 10 xcexcm to 30 xcexcm) in order to prevent deterioration in endurance.
Reference numeral 137 denotes a charge removing brush serving as a charge removing means of the conveying belt 131.
In the above-mentioned configuration, the recording sheet P conveyed from a sheet feeding unit is nipped by the conveying roller 132 and the pinch roller 133 on the conveying belt 131 and is pressed to the conveying belt 131 side by the sheet pressing roller 140.
Then, the recording sheet P is adsorbed on a flat part of the conveying belt 131 by an electric force generated by the adsorption force generating means 136 to which a voltage is applied from the power feeding brush 152.
The recording sheet P adsorbed to the conveying belt 131 is guided to the recording head unit 107 and conveyed in an arrow A direction by the sheet feeding motor 160 and the driving roller 134 while recording an image thereon by the recording heads 107K, 107C, 107M and 107Y.
Charge is removed from the conveying belt 131 by the charge removing brush 137 after it is cleaned by the cleaning roller 138.
The adsorption force generating means 136 will now be described with reference to FIGS. 11 to 13.
FIG. 11 is a schematic view showing the configuration of a conveying belt viewed from an arrow f direction of FIG. 10 and shows an electrode pattern or the like of the adsorption force generating means provided on the conveying belt. FIG. 12 is a sectional view of the conveying belt viewed from an arrow a direction of FIG. 11. FIG. 13 is a sectional view of the conveying belt viewed from an arrow b direction of FIG. 11.
In the figure, the adsorption force generating means 136 are provided inside the conveying belt 131. The adsorption force generating means 136 are composed of electrode plates 136a and ground plates 136b that are made of conductive metal. The adsorption force generating means 136 are formed in a ctenidium (or ctenoid) shape with each tooth provided independently as shown in the figure. A plurality of adsorption force generating means 136 are provided on the conveying belt 131 in such a manner that the respective adsorption force generating means 136 face each other in the direction perpendicular to the belt conveying direction.
On both sides in the moving direction of the conveying belt 131, power fed portions 136axe2x80x2 and 136bxe2x80x2, which expose patterns, respectively, are provided so as to be of a distance longer than the width of respective electrodes 136a and 136b in the belt moving direction. A conductive power feeding brush 152 is provided which contacts each of them with a predetermined pressure.
A positive or negative voltage is applied to the power fed portions 136axe2x80x2 of the electrode plates 136a from a not-shown high pressure power source by this power feeding brush 152. In addition, the power fed portion 136bxe2x80x2 of the ground plates 136b are connected to the earth.
As shown in FIGS. 12 and 13, the conveying belt 131 is provided with the adsorption force generating means 136, which are composed of the electrode plates 136a an the ground plates 136b that are made of conductive metal in adsorption force generating areas, while being protected by being sandwiched by a base layer 136c and a surface layer 136d. The base layer 136c and the surface layer 136d are formed of synthetic resin such as polyethylene and polycarbonate.
When a voltage is given to the electrode plates 136a, an electric force is generated in an arrow direction and an electric line of force shown in the figure is formed. Then, an adsorption force is generated in an upward position on the conveying belt 131 by a potential difference between the electrode plates 136a and the ground plates 136b, which adsorb the recording sheets P. On a recording surface of adsorbed recording sheet P, a charge (surface potential) of the same polarity as the voltage given to the electrode plates 136a is generated.
Further, the adsorption force received by the recording sheet P is the weakest at parts where there is no conductive metal between the electrode plates 136a and the ground plates 136b. 
If a large amount of ink is discharged on the recording sheet P, the recording sheet P swells and cockling occurs. Even in this case, the recording sheet P is adsorbed to the conveying belt 131 side by the adsorption force of the adsorption force generating means 136. Thus, rising of the recording sheet P to the recording head unit 107 side is eliminated, whereby stable recording can be performed without contact of the recording heads 107K, 107C, 107M and 107Y and the recording sheet P.
In addition, the cockling is forced to be scattered to occur in areas where adsorption force on the conveying belt 131 is the weakest (parts where there is no conductive metal between the electrode plates 136a and the ground plates 136b), whereby rising of the recording sheet P to the recording head unit 107 side can be minimized.
In addition, even if the ends of the recording sheet P cockle or curl due to change of environmental factors such as temperature or humidity, the recording sheet P can be pressed to the conveying belt 131 side by the sheet pressing roller 140 to be conveyed to an adsorption force generating area in a state where cockling and curling are removed. Thus, a stable adsorption force can be formed in the recording head unit 107.
FIG. 14 is a schematic perspective view showing a configuration of a platen in accordance with the conventional art.
In the platen 130, ribs 130b, which are disposed in parallel with a belt conveying direction at an arbitrary interval, are on a platen base 130a. An upper surface of each of the ribs 130b is positioned 0 to 0.5 mm below a plane connecting the upper surfaces of the driving roller 134 and the conveying roller 132, thereby regulating the conveying belt 131 so as not to be lower than the upper surfaces of the ribs 130b when the belt rotates.
In addition, the conveying belt 131 is adsorbed to the entire surface of the platen 130 by an electric force that is generated by applying a voltage to the conveying belt 131, so that rotation error or inaccurate conveyance due to increase of rotation loading is prevented.
However, in the case of the above-mentioned conventional art, problems described below occur.
In an ink-jet recording apparatus, it is required to perform conveyance with high accuracy while keeping an interval between a recording sheet and a recording head close and constant in order to obtain an image quality of high definition. In particular, it becomes a factor directly affecting an image quality, in a 1 pass high speed recording apparatus using a line head.
In a recording apparatus in accordance with the above-mentioned conventional art, a conveying belt immediately below a recording head is suspended by the conveying roller 132 and the driving roller 134. Thus, there is a problem that dispersion with a peculiar vibration occurs during high speed rotation that deteriorates an image quality.
In addition, the conveying belt 131 is composed of the adsorption force generating means 136 by ctenidium electrodes consisting of the electrode plates 136a and the ground plates 136b, the base layer 136c and the surface layer 136d, and the layers are joined by such means as adhesives or thermal deposition to each other.
If the conveying belt 131 is left for a long time in a state in which the conveying belt 131 is wound and suspended by the conveying roller 132, the driving roller 134 and the pressure roller 135, wrinkles are left in parts with large curvature abutting each of the rollers due to a difference of curving natures inherent to materials.
When a conveying operation is started, the conveying belt 131 suspended by the conveying roller 132 and the driving roller 134 is pulled in the conveying direction by a tension applied by the pressure roller 135.
However, as shown in FIG. 15, there is a problem in that a peculiar shape remains at a part where a wrinkle is left, and cockling of approximately 0.5 mm to 1.0 mm occurs to deteriorate an image quality in a position opposing the recording head unit 107.
A method of controlling a recording part of the recording sheet P not to be positioned at a remaining wrinkle shape part of the conveying belt 131 is possible. However, in an ink-jet recording apparatus, since an interval between the recording head unit 107 and the recording sheet P is as small as 1.0 mm to 1.5 mm, the recording sheet P rubs a nozzle surface depending on a wrinkle shape, which may cause phenomena such as breakage of a nozzle portion, mixed colors or adhesion due to reactions of inks to make recording impossible.
In addition, as shown in FIG. 16, a method of providing a spur in a position opposing each nozzle to stretch and suspend a conveying belt is also possible. However, this will cause a problem such as deterioration of an image quality or traces of the spur in a high speed recording operation or leakage of a high voltage due to deterioration of a conveying belt surface layer. Thus, this is not suitable for a high speed ink-jet recording apparatus of full-line type.
It is an object of the present invention to provide a conveying apparatus and a recording apparatus with high reliability that can suppress vibration of a conveying belt during conveyance and steadily convey a conveyed object.
It is another object of the present invention to provide a conveying apparatus for adsorbing and conveying a conveyed object by a belt provided with electrodes, wherein the conveying apparatus is provided with applying means for applying a voltage to the electrodes to generate an electric force and belt attracting means for attracting the belt utilizing the force.
Other objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.